Fundamental and 3rd harmonic AC magnetic susceptibility of over-doped polycrystalline Y1-xCaxBa2Cu3O7-delta (x=0.025 and x=0.20) samples

The inter-granular vortex dynamics of two polycrystalline samples Y1-xCaxBa2Cu3O7-? (x = 0.025 and 0.20) with different levels of over-doping is investigated by AC magnetic susceptibility measurements. The temperature dependence of the fundamental and 3-rd harmonic components of AC magnetic susceptibility shows that the sample with higher Ca content and level of over-doping is less influenced by the change of the AC magnetic field amplitude and frequency. The better inter-granular transport properties for sample Y0.80Ca0.20Ba2Cu3O7-? are related to the S-N-S type of the inter-granular links. The observed samples' behavior is compared to the theoretical models of the AC magnetic response of a superconductor. The dynamical processes show a strong effect upon the inter-granular transition for both samples. Finally, a significant temperature misalignment between the imaginary components of the fundamental and 3-rd harmonic AC magnetic susceptibility is observed.